The present invention relates to a method for driving an electro-optical display device such as ferroelectric liquid crystal, dence etc.
Recently, the ferroelectric liquid crystal is drawing attentions of researchers as a successor of the TN type liquid crystal and a display device utilizing such a ferroelectric liquid crystal is currently researched.
The display mode of ferroelectric liquid crystal is categorized into the complex refraction type display mode and guest host type display mode. In the case of driving a display device of such modes, the driving method which has been employed for the conventional TN type liquid crystal cannot be used because the display condition (brightness of display) is controlled by changing the direction of applied electric field, unlike the conventional TN type liquid crystal. Namely, when a voltage, although it may be low level, is continuously applied even in one direction, the ferroelectric liquid crystal may at last respond to such voltage. Therefore, a special driving method is necessary for such display mode.
The driving methods which have been developed so far sometimes allow, during time-shared non-selected period, repeated application of small amplitude pulses having the polarity opposite to that of a pulse for display, and trigger drop of contrast in case that a number of digits to be displayed increases.
Moreover, a voltage to be applied is not a perfect AC voltage and a voltage of the one polarity is applied longer than a voltage of the polarity. Accordingly, there arises a problem that if a device is driven for a long period of time, the transparent electrode for display may be blackened or double color pigment may be discolored or liquid crystal may by deteriorated.
It Since the conventional driving methods are followed by such problems, these methods cannot be considered as the definitive method and therefore advent of the optimum driving method has long been expected.
Moreover, it has been supposed to be difficult to gene rate the intermediate tone in display for the ferroelectric liquid crystal and a driving method for generating the gradation has not yet been developed.